本系列導(dǎo)航：劍指offer（第二版）java實(shí)現(xiàn)導(dǎo)航帖

面試題58.2：左旋轉(zhuǎn)字符串

題目要求：
實(shí)現(xiàn)一個(gè)函數(shù)完成字符串的左旋轉(zhuǎn)功能。比如，輸入abcdefg和數(shù)字2，輸出為cdefgab。

解題思路：
類似于58.翻轉(zhuǎn)單詞順序。首先對于字符串“abcdefg”整體翻轉(zhuǎn)，得到“gfedcba”；然后對于后2個(gè)字符“ba”進(jìn)行翻轉(zhuǎn)，對于剩下的字符“gfedc”進(jìn)行翻轉(zhuǎn)，得到“cdefgab”。

package chapter6;

/**
 * Created with IntelliJ IDEA
 * Author: ryder
 * Date  : 2017/8/18
 * Time  : 16:05
 * Description:左旋轉(zhuǎn)字符串
 * abcdeftg 2 => cdefgab
 **/
public class P286_LeftRotateString {
    public static String leftRotateString(String str,int i){
        if(str==null||str.length()==0||i<=0||i>=str.length())
            return str;
        StringBuilder stringBuilder = new StringBuilder(str);
        reverseSubString(stringBuilder,0,stringBuilder.length()-1);
        reverseSubString(stringBuilder,0,stringBuilder.length()-i-1);
        reverseSubString(stringBuilder,stringBuilder.length()-i,stringBuilder.length()-1);
        return stringBuilder.toString();
    }
    //翻轉(zhuǎn)stringBuilder[start,end]
    public static void reverseSubString(StringBuilder stringBuilder,int start,int end){
        for(int i=start;i<=start+(end-start)/2;i++){
            char temp = stringBuilder.charAt(i);
            stringBuilder.setCharAt(i,stringBuilder.charAt(end-i+start));
            stringBuilder.setCharAt(end-i+start,temp);
        }
    }
    public static void main(String[] args){
        String str = "abcdefg";
        System.out.println(leftRotateString(str,2));
    }
}

運(yùn)行結(jié)果

cdefgab